MOVEMENT OF GAS MOLECULES:
The molecules in the gases have relatively large distance between them.
The molecules in the gases move about very quickly.
A gas molecule moves in a straight line. It changes its direction only when:
it collides with another gas molecule or
with the walls of its container.
After collision it moves away in a new direction. Since gas molecules collide many times each second. Therefore the motion of molecules is constant and random.
PRESSURE IN A GAS:
All the gases exert pressure on the walls of their container.
This pressure is the total force exerted per unit area by the gas molecules on the wall during collision. The gas molecules exert pressure only when they collide with the walls.
Relationship Between the Number of Molecules of Gas and Pressure
Pressure of a gas can be increased by increasing the number of molecules in the container.
If the number of molecules is doubled then number of collisions will also be doubled., hence the pressure is also doubled.
Blowing up a balloon is an example of this. If more air is pushed into the balloon it will be inflated more. Because more air molecules apply pressure on the rubber walls of balloon hence it gets inflated.
Relationship Between the Volume of Gas and Pressure
Pressure of a gas can also be increased by compressing it. This is done by reducing the size of the gas container, which will reduce the volume.
When the gas molecules have been compressed into a smaller volume they will collide more frequently with the walls of container and that creates more pressure.
If the gas is compressed to half its original volume, its pressure will be doubled.
Compressed Natural Gas (CNG) is an example of this. A large amount of gas is squeezed into a small volume to increase the pressure.
VOLUME OF A GAS
Space occupied by substance is known as volume.
The gas has no definite volume because the molecules of the gas are far away from each other and can move freely at high speeds. The forces between the molecules are very small or negligible, therefore gas always takes up the shape and volume of its container.
For example, the smell of a perfume quickly spreads through the room as soon you spray it at your body or clothes. Because, the molecules move freely and randomly at high speeds through out the room.
Volume of a gas can be increased by decreasing its pressure. This could be done by reducing the load on the piston of the gas container. As the gas molecules are in random motion they quickly covers the whole space and the volume increases.
Volume of a gas can be decreased by increasing the pressure. This could be done by increasing the load on the piston of the gas container. Since gases are highly compressible the increased pressure will force the molecules to squeeze together and occupy less space, hence volume decreases.
TEMPERATURE OF A GAS
The temperature of a gas is determined by the average translational kinetic energy of its molecules.
If a gas is heated the average translational kinetic energy of its molecules increases and temperature of the gas rises.
If a gas is cooled down the average translational kinetic energy of its molecules decreases and temperature of the gas falls.
